Analysis of two variant surface antigens from two different isolates continue. Both are cysteine-rich, contain cys-x-x-cys motifs, are highly transcribed, and are found only in the clone expressing the variant. A 170 kD cysteine-rich protein (CRP) has a repeating subunit which was found to contain the epitope which reacts with Mab 6E7. Genes have been identified which can be used to differentiate isolates. One (C4) is highly transcribed in non-WB-like Giardia and is not found in WB-like Giardia. The function of C4 is not known.